1. Field of the Invention
The present invention relates to sterilization processes and more particularly, to hydrogen peroxide sterilization processes.
2. Description of the Prior Art
In equipment where potentially infectious specimens are processed and stored, contamination of the interior surfaces of the equipment and of the contents kept there due to spills and breakage of the specimens is an unfortunate but all too frequent occurrence. Removing the contaminated equipment from a busy laboratory for sterilization is often out of the question. Occasional manual cleaning with surface disinfectants has heretofore been the only practical solution. Another, less practical method of disinfecting, at least for smaller equipment, is to immerse it in glutaraldehyde. In some instances, contamination is so extensive that the equipment is discarded entirely and new equipment purchased to replace it.
Complete, in place sterilization of some laboratory equipment has not been possible, particularly in those items of equipment such as cold centrifuges and refrigerators having very cold interior surfaces or two or more zones of surfaces having widely differing temperatures. For example, some centrifuges maintain specimens at temperatures below 10.degree. C. Other areas within the same centrifuge may be at room temperature.
Hydrogen peroxide in liquid form has long been recognized as a disinfectant. Koubek U.S. Pat. No. 4,512,951 describes a method of sterilization with liquid hydrogen peroxide which includes vaporizing an aqueous solution of hydrogen peroxide and passing the resulting hydrogen peroxide-water vapor mixture into an evacuated sterilization chamber where, upon contact with items to be sterilized, the vapor condenses to form a layer of liquid hydrogen peroxide on the items. The items to be sterilized are maintained at a temperature below the dewpoint of the hydrogen peroxide-water mixture to assure condensation, but the overall chamber temperature must be high enough to prevent condensation of the incoming vapor before it reaches the items. Following a suitable time for sterilization, the condensate is revaporized by passing filtered, preferably heated air over the surface of the items. The Koubek process is useful for sterilizing the cool items in the chamber but does not sterilize the warmer surfaces of the chamber itself.
Similar methods of applying a film of liquid hydrogen peroxide over an area to be sterilized and vaporizing the film by flowing heated air over the area are disclosed in Egger U.S. Pat. No. 3,904,361 and Lothman et al. U.S. Pat. No. 4,225,556.
Sterilization with gaseous hydrogen peroxide is described by Moore et al. U.S. Pat. No. 4,169,123 and Forstrom et al. U.S. Pat. No. 4,169,124. The methods described in those two patents involve surrounding an article to be sterilized with vapor phase hydrogen peroxide and maintaining contact between the article and the sterilant at temperatures below 80.degree. C. until sterility is achieved. The lowest temperature disclosed in either the Moore or Forstrom patents is 20.degree. C. The vapor phase hydrogen peroxide is removed from the chamber following the sterilization cycle by evacuation. A uniform temperature throughout the sterilization chamber is contemplated by the methods of the Moore and Forstrom patents.
While the prior art methods of sterilization with hydrogen peroxide are useful in some environments, they do not contemplate environments such as a cold centrifuge or refrigeration equipment which have two or more zones of widely differing temperature ranges within the same piece of equipment. In these environments, where potentially contaminating specimens are processed or stored, spills routinely occur. In the centrifuge, airborne contamination is common. It would be desirable to sterilize the interior of the equipment before having to open it to remove the contents to spare the technician the risk of exposure to contamination. It would also be desirable to sterilize without altering the temperatures within the equipment to maintain specimens at the desired temperature.
There was, prior to the present invention, no convenient method for sterilizing equipment having two or more zones of widely differing temperature ranges within the same chamber without substantially altering those temperature ranges. The known hydrogen peroxide sterilization methods either heat cool surfaces to revaporize liquid sterilant for removal, as in the Koubek patent, or contemplate a uniform temperature throughout the chamber, as in the Moore and Forstrom patents.
It is an object of the present invention to provide a process for sterilizing surfaces within equipment, such as cold centrifuges or refrigerators, having very cold portions without significantly elevating the temperature of the cold portion of the surfaces. It is a further object of the present invention, to provide such a process where two or more surface portions in the same chamber, each having widely differing temperature ranges, can be simultaneously sterilized without significantly altering the temperature of any surface portion.